A polydimethylsiloxane modified with alkyl groups having 2 to 30 carbon atoms (hereinafter referred to as “an alkyl-modified polydimethylsiloxane”) combines properties of both a silicone and an alkane and is characterized by excellent characteristics, such as lubricity, humectant (vapor obstructive) properties, adsorption residual properties, etc.
Alkyl-modified dimethylpolysiloxanes, especially those liquid polydimethylsiloxanes that are modified with alkyl groups that contain 4 to 18 carbon atoms, are superior in their handling properties to wax-type dimethylsiloxanes modified with long-chain alkyl groups, possess excellent emulsifiability and emulsion stability when used as oiling agents in emulsification systems of cosmetic products, and demonstrate pleasant coating sense and water repellency. Therefore, it is expected that such alkyl-modified dimethylsiloxanes will find wide application in the manufacture of shampoos, rinsing, hair-treatment, and sun-screen products, moisturization creams, or similar products (see, e.g., Patent References Nos. 1 to 3).
Generally, alkyl-modified polydimethylsiloxane is synthesized by a hydrosilation reaction (addition reaction) between polydimethylsiloxane having hydrosilyl groups (Si—H groups) and α-olefin in the presence of a platinum catalyst. However, an alkyl-modified polydimethylsiloxane synthesized by the above-described method is characterized by a specific (rather unpleasant) odor. One of the causes of this odor is α-olefin, which is used in an excessive amount during synthesis, remains as a residue in the reaction product (crude product), and generates an odor when oxidized. Patent Reference No. 3 discloses a method for producing a purified alkyl modified polydimethylsiloxane which is rendered substantially odorless by subjecting a crude product of an alkyl-modified polydimethylsiloxane to a hydrogenation reaction in an organic solvent such as an alcohol-type solvent, an ethyl-type solvent, or the like and in the presence of an hydrogenation catalyst. The aforementioned reference also discloses a cosmetic material that contains a purified product obtained by the above method.
However, a purified product of an alkyl-modified polydimethylsiloxane obtained by the above method overcomes the scent (unpleasant odor) odor only for a limited time and since such an odor significantly affects quality and applicability of cosmetic products, further improvement in odor-elimination properties is required.    [Patent Reference 1] JP 2003-012466 A    [Patent Reference 2] JP 2003-048813 A    [Patent Reference 3] JP 2005-232235 A